Devices for producing bags from a foil strip are already known wherein the foil strip is folded along its center line to form a half tube such that the two halves are mated with each other. The two layers are then connected together by means of transverse bonded seams and individual bags can be separated in succession from the chain of bags thus formed. An advancing device is provided between the bonding device and the separating device so as to move the foil strip between these two devices. The advancing device pulls the foil strip in the region in front of and after the bonding device and only pushes the end of the strip in the region of the separating device. With devices of this type it is possible to process packing materials comprising a supporting layer and an inner heat sealing layer into bags without any difficulty. However, if thermoplastic packing materials are being processed which become soft or melt along their entire cross-section at the necessary bonding temperature, it is only possible to use the process employing the known devices if the bonded seams have cooled sufficiently before pulling stresses are applied by the advancing device so that they do not rip or stretch. This problem can generally be solved by employing a heat pulse bonding process wherein the seam regions are not only heated to the bonding temperature but are also cooled to a large extent. A disadvantage of using this heat pulse bonding process consists in that the device has a very low capacity because, in addition to the bonding and transporting time, additional time is required to cool the bonded seams. The thicker the packing material, the greater the drop in output.
To obviate this disadvantage, the Auslegeschrift No. 1,484,982 proposed a pair of endless conveyor belts, the belt sections of which are turned towards each other and support the foil layers with respect to the bonding and cooling elements and through which the bonding heat is transferred to the packing material. A device of this type is costly and still does not have the capacity which can be obtained with the above-described devices when using multi-layer packing materials, as heat must be transferred through the conveyor belt onto the packing material.